Method of rational large volume CVD production

ABSTRACT

The present invention relates to a method to rationally coat cutting tool inserts comprising a substrate and a coating deposited using a CVD and/or MTCVD method. According to the invention the inserts are positioned on a net with a surface roughness, R a , of the wires between 2 and 50 μm.

BACKGROUND OF THE INVENTION

The present invention relates to a method of coating large volumes ofcutting tools (indexable inserts) for machining by chip removal in arational and productive manner, which inserts contain hard and wearresistant refractory layers deposited by CVD (Chemical Vapor Deposition)and/or MTCVD (Moderate Temperature Chemical Vapor Deposition). Themethod is based on the use of a woven metal net with a certain surfaceroughness. In this way, it has been found possible to reduce thedrawbacks of the prior art methods.

CVD-deposited wear resistant coatings, particularly of TiC, Ti(C,N), TiNand Al₂O₃ on cemented carbide inserts have been industrially producedsince the beginning of the 1970's. Details regarding the depositioncondition of CVD and/or MTCVD coatings and the design of CVD and/orMTCVD based coatings have been extensively discussed in the literatureas well as in patents.

One of the major advantages of the CVD and/or MTCVD technique is thepossibility of coating very large numbers of tools in the same batch, upto 30,000 inserts depending on the size, which gives a low productioncost per insert with a coating all-around the insert. In order to obtaina uniform coating thickness distribution, it is important thatfunctional surfaces of the inserts are relatively equally separatedduring the coating operation. However, during the coating operation notonly the tools are coated but also the support on which the tool restsresulting in that the insert grows together with the surfaces of thesupport. When the inserts are removed after the coating cycle isfinished, contact marks appear at those spots.

These contact marks are not only a cosmetic problem. If they appear onsurfaces actually in operation during the metal cutting operation, theymay lead to a decreased tool life. In addition, the support surfaces onan insert must be flat, without protruding marks, in order to avoiderroneous positioning of the insert in the tool holder. An erroneouslypositioned insert will negatively influence the performance of thecutting tool, i.e., decreased toughness and changed accuracy and surfacefinish of the work piece. In order to minimize the negative effect ofthe contact marks, several complicated arrangements have been reportedwhere objective is to move the marks from the functional surfaces toother areas.

Another important aspect on such a system for batch loading of CVDand/or MTCVD coated inserts is that it has to be very flexible tocompensate for the difference in insert style. A typical standard CVDand/or MTCVD coating is deposited onto inserts of different size varyingfrom 5 mm in inscribed circle up to 50 mm. The shape of the insertvaries, e.g., rectangular, octohedrical, square, round, triangle,diamond, etc. The insert can be with or without a central hole and withdifferent thickness varying from 2 mm up to 10 mm. One type of a CVDand/or MTCVD coating cycle will therefore be deposited onto as much ashundreds of different styles of inserts all needing differentarrangements. Therefore, a batch loading system which necessarily needsdifferent arrangement for different insert styles in order to get auniform loading density will never work very rationally in a productionenvironment focused on low cost and short lead time.

EP 454,686 discloses a loading system, particularly aimed for PACVD,where in the inserts are stacked on top of each other on a central pinwith or without a spacer between. Using this method for CVD and/or MTCVDyields several disadvantages as it is not a universal method, asdescribed above, since different styles of inserts will need differentset-up of the pins. Secondly, a hole is needed on the inserts. Third,when applying thick CVD and/or MTCVD coating the inserts will probablyheavily get stuck to the spacer and/or other inserts due to the pressurefrom the above position inserts which will enhance the tendency to growtogether.

U.S. Pat. No. 5,576,058, U.S. Pat. No. 5,759,621 and SE 940,0950disclose a batch loading system based on different arrangement of pegscomprising a foot portion, a shoulder portion, a neck and a head. Thisbatch loading system will never be very flexible or rational asdescribed above since different styles of inserts will need differentset-up of pegs.

A commonly used loading arrangement is to place the inserts into holesor slits in a tray. This method will give contact marks on the cuttingedge or on clearance faces of the inserts. Using this arrangement needsalso a very careful handling during transportation and loading of thetrays in order to avoid that the inserts fall out of their positions.This arrangement is also very difficult to use when automated insertsetting is used since the inserts shall be put in very unstablepositions.

In yet another method, the inserts are threaded up on a rod. The rodsmay be vertically arranged as in EP 454,686 with the same disadvantagesas discussed above, or horizontally. The main drawback of thehorizontally arrangement is the lack of universality for differentinsert styles, which is why necessarily a large number of differentset-ups are needed in order to produce all styles of inserts.Additionally, this method can only be applied to inserts with a hole.

The most universal arrangements are based on simply placing the insertson a surface separated with necessary spacing in-between either on wovenmetal nets or on some other surface (often made of graphite). The loadis built up by piling each metal net on top of each other separated bysome distance or using some graphite carrier onto which the nets arepositioned. The great drawback with this method so far has been contactmarks between the nets and the inserts that always are formed. Thesemarks give an incorrect positioning of the insert in the tool holder andmay give seriously decreased performance of the inserts. Often, somepost-treatment may be needed in order to remove protruding marks. Alsomarks may be found on the cutting edge which also is very negative forinsert performance. Another disadvantage with using woven nets is thatinserts relatively easily may slide together before deposition therebyresulting in uncoated areas on the inserts.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of this invention to provide a CVD and/or MTCVD batchloading system which allows a rational production method without a largenumber of different arrangements depending on different insert stylesi.e., a universal, insert style independent system.

It is further an object of this invention to provide a CVD and/or MTCVDbatch loading system which avoids the problems of the prior art batchloading systems based on woven metal nets, i.e., contact marks and/orthat inserts slide together prior to or during deposition.

In one embodiment of the invention there is provided in a method torationally coat cutting tool inserts comprising depositing a coating ona substrate using a CVD and/or MTCVD method, the improvement comprisingpositioning the inserts on a wire net with a surface roughness, R_(a),of the wires of between 2 and 50 μm.

In another embodiment of the invention, there is provided a woven metalnet wherein the surface roughness, R_(a), of the wires is between 2 and50 μm.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a SEM (Scanning Electron Microscope) image of a Mo-wire from anet pre-coated with approximately 5 μm CVD and MTCVD coating ofTi(C,N)+Al₂O₃+TiN.

FIG. 2 is a SEM image of a Mo-wire from a net which prior to first timeuse has been spray-coated with approximately 50 μm thick Mo-layer andsubsequently pre-coated with approximately 5 μm CVD and MTCVD coating ofTi(C,N)+Al₂O₃+TiN according to the present invention.

FIG. 3 is a LOM (Light Optical Microscope) image of a cross section of aMo-net with radius, measure a, that has been spray-coated with aMo-layer, which thickness is defined by the measure b.

DETAILED DESCRIPTION OF THE INVENTION

In the following description we will use terms as follows:Spray-coating(s) define(s) a coating preferably applied by a sprayprocess as thermal sraying, plasma spraying etc. Pre-coating(s)define(s) a CVD and/or MTCVD-coating applied onto the net or supportmaterial before first time use in the deposition of wear resistant CVDand/or MTCVD coatings onto the final product, herein defined asproduction-coating(s).

The critical size of the protruding marks, where they start to influencethe properties of the tool, used in the following description as thelimit for approval or rejection of an insert is a maximum height of 20μm.

According to the present invention, it has surprisingly been found thatif the surface of a woven metal net is provided with a certain surfaceroughness, it is possible to avoid large contact marks and in particularto avoid protruding marks. This optimal surface structure essentiallyeliminates the problems of the prior art.

According to present invention, the surface roughness, R_(a), of the netis between 2 and 50 μm, preferably between 3 and 20 μm.

The woven metal nets may be made of metals as Fe, Ni, Mo, Cr, Ta, Ti, Wor alloys thereof. Also other materials from which a net is possible toproduce could be used provided that they have a sufficient strength at1000° C. Preferably, the woven nets are made of Fe, Mo or alloysthereof. The nets shall have a mesh size, defined as the number ofequally spaced openings per linear inch, which allow a uniform gas flow,and an optimal wire diameter to get sufficient strength and optimalnumber of contact marks. The mesh size of the unused net is preferablybetween about 5 and 12. The wire diameter is preferably between about0.3 mm and 1.2 mm.

In a preferred embodiment, a surface with the desired surface roughnessis obtained by depositing a coating thereon using spray-coatingdeposited by the use of plasma spraying, thermal spraying and othersimilar techniques. The spray-coating process could be of either warm orcold type.

The spray-coating(s) may be deposited onto both sides of the net, but itis necessary only on the side aimed to be in contact with the inserts.

The sprayed coating(s) comprise(s) metals such as Fe, Ni, Mo, Cr, Ta,Ti, W or alloys thereof. Also, other materials like oxides, carbides andnitrides are possible and/or composites between metal(s) and orceramic(s). Preferably, the spray-coating is made of Fe, Mo or alloysbased on those metals. In order to obtain a good adhesion between thenet, or support material to the spray-coating, it is an advantage if theratio, k, between the coefficients of thermal expansion of the net (orsupport) material, an, and the spray-coating, as, is between 0.5 and1.5.

Prior to deposition of the spray-coating, it is important that the netis properly cleaned. Pre-treatment of the uncoated nets involvingmechanical cleaning as dry and/or wet blasting could also offeradvantage by enhancing the adhesion of the coatings.

The spray-coating(s) layer can be deposited directly onto the metal netas a single layer or as multilayer consisting of different materialsmentioned above. Also, a first intermediate CVD and/or MTCVD coatingbased on TiC and/or Ti(C,N) and/or Al₂O₃ layer(s) could be depositedonto the metal net before any spray-coating(s) are deposited.

The total average coating thickness of said spray-coating(s), on theside in contact with the inserts is between 5 and 300 μm, preferablybetween 25 and 200 μm. FIG. 3 shows a LOM polished part of a crosssection of a Mo-net with radius of 450 μm (the measure a) which isspray-coated with 50 μm thick Mo-layer (the measure b) according topresent invention. This figure clearly shows the unevenness of thespray-coating which offers the advantage of smaller contact pointsbetween the insert and the net which in turn results in smaller and lessprotruding contact marks. It can also be seen in the figure thedifficulties in discussing and/or specifying the exact coating thicknessof the spray-coating(s) due to unevenness while only some rough averagevalue can be given.

Table 1 shows the influence on the surface roughness from the usage ofthe nets. Using an optical interference measurement device, measurementsof the surface roughness were made. The Mo-wire pre-coated with a CVDand MTCVD coating of Ti(C,N)+Al₂O₃+TiN of a total thickness of 5 μm,variant a, resulting is a surface roughness R_(a) of 0.3 μm. Variant cin table 1 is a Mo-wire coated with a sprayed Mo-coating of thickness 50μm and pre-coated with a CVD AND MTCVD coating of Ti(C,N)+Al₂O₃+TiN of atotal thickness of 5 μm giving, the spray-coating process changed thesurface roughness R_(a) to a value of 11 μm. The variants b and d intable 1 correspond to variant a and c but after additionally fourproduction coating cycles of all together approximately 25 μm CVDTi(C,N)+TiC+TiN coating resulting in a surface roughness of 0.4 μm and8.9 μm, respectively. It is worth noting that the surface roughness hasstayed rather unaffected for the spray-coated net as well as for theunspray-coated net during usage, but at different levels of surfaceroughness. TABLE 1 R_(a), R_(t), maximum R_(p), maximum arithmeticprofile depth, profile height, top mean value top to bottom to medianline Net variant (μm) (μm) (μm) a, (Mo-net, pre-coated) 0.3 2.9 1.4 b,(Mo-net, pre-coated, 0.4 3.8 1.7 production-coated four times) c, (Spraycoated Mo- 11 51 31 net, pre-coated) d, (Spray coated Mo- 8.9 39 24 net,pre-coated, production-coated four times)

Before use for production-coating, the spray-coated net is preferablypre-coated with a CVD and/or MTCVD coating based on TiC and/or Ti(C,N)and/or Al₂O₃ and/or TiN, single or multi-layers, of a total coatingthickness between 2 and 150 μm, preferably between 5 and 50 μm.

Post annealing, or intermediate annealing, in an inert or reactiveatmosphere of the spray-coated nets could also be used in order toincrease the performance by enhancing the coating adhesion.

The desired surface structure could also be produced using other coatingtechnologies.

In another embodiment, the desired surface roughness is obtained byetching of the nets in a suitable medium. This method is in particularapplicable to nets made of a multiphase material such as some stainlesssteels.

In yet another embodiment, the desired surface roughness is obtained bymechanical methods such as blasting.

The present invention has been described with reference to inserts butit is obvious that it also would be beneficial for the processing ofother types of coated components, e.g., drills, end-mills, wear parts,etc.

In another embodiment, the woven metal net to be spray-coated isexchanged to material with an optimized-designed surface, i.e., metalsheet with a pattern of pressed holes and protruding tips.

The invention is additionally illustrated in connection with thefollowing Examples, which are to be considered as illustrative of thepresent invention. It should be understood, however, that the inventionis not limited to the specific details of the Examples.

EXAMPLE 1

A woven Mo-net with a wire diameter of 0.9 mm and a mesh size of 7 waspre-coated with a CVD and MTCVD coating of Ti(C,N)+Al₂O₃+TiN of a totalthickness of 5 μm. The wires had a surface roughness R_(a) of 0.3 μm,see FIG. 1 and Table 1 variant a, here designed variant A.

The same type of net as used for variant A, was coated with anapproximately 50 μm thick spray-coating of Mo onto the Mo-net prior tofirst time use. The net was thereafter pre-coated with a CVD and MTCVDcoating of Ti(C,N)+Al₂O₃+TiN of a total thickness of 5 μm. The surfaceroughness, R_(a), was 11 μm, see FIG. 2and Table 1 variant c, heredesigned variant B.

Cemented carbide inserts of style XOMX0908-ME06 with composition 91 wt %WC-9 wt % Co were used. Before deposition the uncoated substrates werecleaned. A CVD production-coating of Ti(C,N)+TiC+TiN with anapproximately 5 μm total coating thickness was deposited on the inserts.Totally ten nets per variant were used and onto each of the wovenMo-nets 330 inserts were positioned. After production-coating, 5% ofrandomly picked inserts from each net were checked for contact marks. Ifthe marks were of protruding type, the maximum height of the protrusionswas measured with an optical Nikon device. If more than one protrudingmark on one insert were found the maximum height was taken as themeasure of the actual insert. Depending on the height of the protrudingmark the inserts were classified into four different classes;

-   Class 1: No marks-   Class 2: Marks<10 μm-   Class 3: 10 μm<Marks<20 μm-   Class 4: Marks>20 μm, Not approved.

Inserts measured were coated in first production-coating cycle afterpre-coating. Table 2 below summarizes the results. TABLE 2 Variant AVariant B Mean (μm) 20 7 Standard deviation (μm) 4 6 Minimum (μm) 10 0Maximum (μm) 28 19 Class 1 (%) 0.0 23.8 Class 2 (%) 1.9 45.6 Class 3 (%)56.2 30.6 Class 4 (%) Not approved 41.9 0.0

It can clearly be seen that variant B got much less and smaller marks.By using the present invention all inserts are approved, i.e.,protruding marks smaller than 20 μm, while using prior art 42% are notapproved.

EXAMPLE 2

The same nets as in example 1 were tested using the same analyzing andclassifying method but after additionally three production-coating cycle(totally production coated four times). Variant C corresponding tovariant A (in example 1) but used for a longer time has still a lowsurface roughness R_(a) of 0.4 μm, see Table 1 variant b. In the sameway corresponds variant D, with a surface roughness R_(a) of 8.9 μm tovariant B (in example 1), see Table 1 variant d. The inserts measuredand classified were coated in production-coating cycle number five afterpre-coating. All production-coating cycles were of same type as inexample 1. The total production-coating thickness is approximately 25μm. Table 3 below summarizes the results. TABLE 3 Variant C Variant DMean (μm) 17 8 Standard deviation (μm) 9 3 Minimum (μm) 5 0 Maximum (μm)52 17 Class 1 (%) 0.0 0.9 Class 2 (%) 24.4 78.9 Class 3 (%) 47.9 20.2Class 4 (%) 27.7 0The variant C, which is according to prior art, works somewhat betterthan in example 1 but still 28% are not approved. By using the presentinvention all inserts are approved.

EXAMPLE 3

The same variants of nets as in example 1 were tested using the sameanalyzing and classifying method. A thicker CVD coating, total coatingthickness of 8 μm, including a 3 μm thick Al₂O₃ layer, was grown ontothe substrates. The insert style was CNMG120412-MF2. Inserts measuredwere coated in production-coating cycle number five after pre-coating.The surface roughness, R_(a), prior to this production-coating isestimated to be rather similar as in example 2, i.e., approximately 9 μmand 0.5 μm, respectively. Table 4 below summarizes the results. TABLE 4Variant E Variant F Mean (μm) 17 9 Standard deviation (μm) 4 3 Minimum(μm) 6 0 Maximum (μm) 30 17 Class 1 (%) 0.0 1.9 Class 2 (%) 6.9 65.0Class 3 (%) 75.6 33.1 Class 4 (%), Not approved 17.5 0.0It can clearly be seen that the spray-coated variant F got much less andsmaller marks. Also in this example by using the present invention allinserts are approved, while using prior art 18% are not approved.

The principles, preferred embodiments, and modes of operation of thepresent invention have been described in the foregoing specification.The invention, which is intended to be protected herein, however, is notto be construed as limited to the particular forms disclosed, sincethese are to be regarded as illustrative rather than restrictive.Variations and changes may be made by those skilled in the art withoutdeparting from the spirit of the invention.

1. In a method to rationally coat cutting tool inserts comprisingdepositing a coating on a substrate using a CVD and/or MTCVD method, theimprovement comprising positioning the inserts on a wire net with asurface roughness, R_(a), of the wires of between 2 and 50 μm.
 2. In themethod of claim 1 wherein the surface roughness, R_(a), of the wires isbetween 3 and 20 μm.
 3. In the method of claim 2 wherein the net hasbeen coated with a spray-coating with an average thickness between 5 and300 μm on the side to be in contact with the inserts.
 4. In the methodof claim 3 wherein the spray-coated net has been pre-coated with a CVDand/or MTCVD coating based on TiC/Ti(C,N)/TiN/Al₂O₃ of a total thicknessbetween 2 and 50 μm.
 5. In the method of claim 4 wherein the netmaterial is made of Fe, Ni, Mo, Cr, Ta, Ti, W or alloys based thereof.6. In the method according to claim 5 wherein the net material is Fe, Moor alloys based thereof.
 7. In the method of claim 4 wherein thespray-coating material is Fe, Ni, Mo, Cr, Ta, Ti, W or alloys basedthereof.
 8. In the method of claim 7 wherein the spray-coating materialis Fe, Mo or alloys based thereof.
 9. In the method of claim 2 whereinthe surface roughness is obtained by etching and/or mechanicaltreatment.
 10. A woven metal net wherein the surface roughness, R_(a),of the wires is between 2 and 50 μm.
 11. A woven metal net of claim 10wherein the wires are made of Fe, Ni, Mo, Cr, Ta, Ti, W or alloys basedthereof.
 12. A woven metal net of claim 11 wherein the wires are made ofFe, Mo or alloys based thereof.
 13. A woven metal net of claim 10wherein the surface roughness of the wires is between 3 and 20 μm.
 14. Awoven metal net of claim 10 wherein the wires are coated with a CVDand/or MTCVD coating based on TiC/Ti(C,N)/TiN/Al₂O₃ of a total thicknessbetween 2 and 50 μm.